The troubled Mid Staffordshire NHS foundation trust may become the second in the country to be placed in special administration after experts were sent in by the regulator to find a solution to its financial problems.

Monitor, the independent regulator, said it was sending in a team to secure the two trust hospitals' finances after hard work to sort out its clinical issues. Mid Staffs became a byword for poor care after an independent inquiry in 2009 found that patients had been neglected and some had died as a result. A second, full public inquiry by Robert Francis QC into what happened there between January 2005 and March 2009 is due to report to the health secretary next month. Some staff have been officially warned that they will face serious criticism.

The trust has been in financial straits for some time, with a deficit of £19.9m in the last financial year.

"We have been working closely with Mid Staffordshire NHS foundation trust to improve its performance," said Dr David Bennett, chair and interim chief executive of Monitor. "It has made significant improvements in the clinical care provided for patients, but we need to make sure these services can be secured in the long term.

"It is therefore time for us as the sector regulator to step in and look for a solution that ensures services are provided for local patients on a sustainable basis. We have an open mind about the form that solution might take, but it should be the best one for patients in the long term."

One option could be a solvent restructuring of the trust, said Monitor. Another could be special administration – as happened with the South London healthcare trust, which reported a deficit of £65m last year. South London's administrator, Matthew Kershaw, has asked private companies if they would be interested in running its services.

Lyn Hill-Tout, chief executive of Mid Staffordshire NHS foundation trust, said: "We are hopeful that the outcome of this review by Monitor will be that decisions are made about which services are to be provided at Stafford and Cannock Chase hospitals.

"Reviews of the trust over the last few years and the changes to the way healthcare has begun to be provided nationally have led to a growing feeling of uncertainty about the future of the two hospitals."

Julie Bailey, founder of Cure the NHS, the campaigning group representing Mid Staffordshire patients, said the investigation was "another serious blow to our hopes that Mid Staffs was getting its act together". Hundreds of people had lost their lives, she claimed, because the hospital management, at the instigation of the Labour government, was more concerned about keeping the budget down than ensuring patient safety.